There is currently a large and growing requirement of NF.sub.3 for use in semiconductor manufacturing. Methods of producing NF.sub.3, however, are not nearly as efficient as theoretically possible which is shown by current syntheses' poor efficiency of utilizing expensive F.sub.2. The two principle methods, electrochemical fluorination (ECF) and direct fluorination (DF), have yields less than 50% of theory and most typically in the range of 30-45%. These yields are based on the equivalents of F.sub.2 used in the process. In the direct fluorination of NH.sub.3 or NH.sub.4.sup.+ salts to produce NF.sub.3, there are competing reactions as follows: EQU 3F.sub.2 +NH.sub.3 .fwdarw.NF.sub.3 +3HF (1) EQU 3F.sub.2 +2NH.sub.3 .fwdarw.N.sub.2 +6HF (2) EQU 4F.sub.2 +2NH.sub.3 .fwdarw.N.sub.2 F.sub.2 +6HF (3)
The most favored reaction according to thermodynamic calculations is (2), which produces only undesirable N.sub.2 and HF. The prior art has attempted to enhance reaction (1) to produce NF.sub.3 and minimize the extent of reactions (2) and (3). Previous attempts to produce NF.sub.3 by the direct fluorination of NH.sub.3 in liquid ammonium acid fluoride resulted in yields of 30 to 63%.
Currently the most efficient process for producing NF.sub.3 is U.S. Pat. No. 4,091,081. It involves the direct fluorination of ammonium ions by F.sub.2 whereby gaseous F.sub.2 is contacted with liquid (molten) ammonium acid fluoride (AAF) while gaseous NH.sub.3 is separately contacted with the liquid AAF to generate ammonium ions. This process typically gives NF.sub.3 yields of 40-50%. It is operated to maintain a molar ratio of by-product HF to ammonia of 2.0 to 2.5 (melt ratio) in the reaction liquid and at temperatures above the melting point of ammonium bifluoride, NH.sub.4 HF.sub.2, which is 127.degree. C. The contacting of F.sub.2 with AAF is done using a specially designed sparger having a plurality of small holes. The most significant shortcoming of this process is the low selectivity and yield of NF.sub.3.
U.S. Pat. No. 4,543,242 discloses a synthesis of NF.sub.3 using gaseous fluorine and solid (NH.sub.4).sub.3 AlF.sub.6. The yield of NF.sub.3 was in the range of 65-78% based upon fluorine.
Japanese Patent Kokai 03-232710 discloses the synthesis of NF.sub.3 from a metal fluoride, an inorganic ammonium salt and elemental fluorine.
Gas phase reactions of ammonia and fluorine are described in Japanese Patent Kokais 02-255511; 02-255512 and 02-255513. In the former Kokai, an NF.sub.3 yield of 43.7% is reported.
The prior art has failed to produce nitrogen trifluoride in yields in the range achieved by the present invention. With the increased demand for nitrogen trifluoride from the electronics industry, a need has arisen to utilize larger nitrogen trifluoride production plants. At the higher energy and capital costs of such larger production plants, it is increasingly important to achieve the highest yields possible from the reaction synthesizing nitrogen trifluoride. The present invention achieves these high yields as will be set forth in greater detail below.